The invention relates to a heater device applicable to desiccant rotor dehumidifier. The working principle of a desiccant rotor dehumidifier is shown in FIG. 1, the dehumidifier D mainly includes a heat-exchanger (water condenser) 1, a desiccant wheel 2, a first fan 3, a second fan 4, a heater device 5 and a tank 6. The drawing does not show the case, frame and control device. An exterior airflow A0 driven by the first fan 3 passes the exterior of the heat-exchanger 1 (airflow A1), a humidity-absorbing region 22 of the desiccant rotor 2 (airflow A2) and blown out through the first fan 3 (airflow A3). An internal airflow driven by the second fan 4 (airflow B4) passes through the heater 5 (airflow B1), a regeneration region 21 of the desiccant rotor 2 (airflow B2), the interior of the heat-exchanger 1 (airflow B3) and returns to the second fan 4 and cycles. The heat-exchanger 1 is mainly a hollow plastic or metallic tube (manifold) member having an inlet 110 and an outlet 12 connecting respectively to the regeneration region 21 of the desiccant rotor 2 and an inlet of the second fan 4 so that the warm and humid airflow A3 inside the manifold and the airflow A0 passing through exterior of the manifold takes heat-exchange. Water 16 is then condensed and collected to the tank 6. The desiccant rotor 2 is a disc-like honeycomb ceramic substrate coated or compounded with desiccant (usually zeolite or silica gel). An unshown driving unit drives the desiccant rotor (in direction R as illustrated) with a suitable speed turning into the regeneration region 21 (corresponding to the heater 5 position) and out for the humidity-absorbing region 22. At the humidity-absorbing region 22, the exterior airflow A1 passing through the honeycomb pores of the desiccant rotor 2 leaves humidity in the desiccant. Then, at the regeneration region 21, the humidity in the rotor 2 is dried out by the circulated airflow passing through the heater 5 (the warm airflow B1) and becomes warm and humid airflow B2 to be condensed in the heat-exchanger 1 after passing through a collector 11 into the heat-exchanger 1. The relatively dehumidified airflow B3 is further driven back by the second fan 4 (airflow B4) and expelled into the heater 5 to become warm airflow B1 for regenerating the desiccant rotor 2. So the cycles proceed.
The heater device mainly includes heating wire or similar elements for heating the airflow. In order to improve heating efficiency, the airflow output has to be uniform for the regeneration region, and prevented from external thermal loss. FIG. 4 is a prior heater device disclosed in Japan Laid-open Patent No. 2003-38930. The heating unit 9 includes a heating element 9a installed inside a case 9b. A blower (fan) 7 provides warm air via the heating element 9a to a desiccant rotor 2. A shield plate 9c located between the heating element 9a and the case 9b shields the direct thermal radiation of the heating element to the case. The shield plate 9c keeps an air gap to the case 9b so as to decrease indirect thermal loss. The shield plate 9c has shiny surface for reflecting the thermal radiation of the heating element 9a. An inclination 9e is formed on the shield plate 9c to guide the airflow toward the heating element 9a. Though the construction can save thermal loss, the airflow passing through the heating element 9a is not controlled of its uniformity. Further, the shield plate 9c is usually made of metal. As a result, the supporting means for the heating element 9a (usually bare heating wire) have to be well electrically insulated that cause the assembly more complicated and costly.
Therefore, it is a great demand to have a heating device with simple structure, less thermal loss and uniform airflow output.